Add shadow sampler LOD tests Added tests for GLSL 3.00 shadow samplers in fragment shaders with TEXTURE_2D target. Bug: angleproject:365066518 Change-Id: I5b93d030cd14a388541acaff9f7a707ad599dba3 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5845491 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>